Oxygen detection and measurement



Jar'l- 3, 53 E. 1.. KELLS ETAL 2,62

OXYGEN DETECTION AND MEASUREMENT Filed July 15, 1949 INVENTOR S "pLxmu.

Patented Jan.

West Hollywood Calif.

nitration-11y '13, 1949, Serial No. 104516 from combustion process es',,gives an indication of the efiiciency of the combustion; many chemiealpr se n o in -i'sas ous reactions n e pend for proper control upon theoxygencontent. of the feed or output, gases; where air isused o s pportl e ndh abil yofho sy en depl tion is present the necessity of knowingthe oxygen concentration is QbY DuSM. .p v. c 4 all c a plieatie s it sighl vadva ta ous, d, enera y .abs ut yc e essary, to have t e a a ic l.r suitsimmedia y a ai ab e. While oxy e conc n ati ns. b det rmi e y ndhem ea me h ds. of as. analysis,v the delay introduced thereby generallyrenders the analysis useless asitisthen'too late to make y nd at haes.,.in,.-Qpe in condition Accordingly,- many devices have beendeveloped which s r ,.o ..'by oneme nsor ot n: a ap d an si iof.a.sasforr xy en. and ally provide e esu tn n nehiorm t at it can becontinuously recorded; ,Unfoitl natelymost such devices are mechanicallycomplex; depending as they do upon characteristics of oxygen notjreadilyadaptable to simple and foolproof; measure ment, and thus notonly areexpensive but require expert attention. v p. v ,I

At the same timejitis not onlynecessary; to w W a t e xygen c c ntr ionst environments m nti ned. as. ex mplesic t it; i also hi ad anta eous;inim id .v mea se ticularly adapted to simple mechanical embo'di-Another object of the invention is to provide new and novel means. 0controlling oxyeenconcentrations" and processes dependent upon thelatter.

r; chins. 1.17am) 2 Another object of the invention is to providea meansof/ determining oxygen concentrations instantaneously. s

, Other .objectsof the invention will appear as thedescriptionthereofproceeds so vBroadly stated; according to the presentinven-, tion thei'oxygen content ofa; gas isfound (and if desired,controlled); by determining; directly or by a: function thereof,- themagnetic susceptibility ofthe gas in, question andrelating the value, sofound,v to the. oxygen contenthIt is possible to do .,this1'b'e'cause;,of all the :.gas,es commonly occurringiin the fieldsof applicationofthis. invention' oxygen isthe only one possessing paramagnetism;,a1l,other.commonly ,occurring gases, such as, nitrogen carbon dioxide;carbon monoxide, sulfur, dioxide, sulfur v.trioxide;,.hy1.irogen andgaseous hydrocarbons, ,are diamagnetia. (More- 1 over; theabsolutevalue. of the volume magnetic susceptibility of oxygen-;,.thatis, susceptibility per unitvolume), is morethan times vthat of. mostothercommon gases, and inufactis about ZSQHti'mes that of ,the non-foxygen, portion of ordinary flue gases. The following values are c e-fnm e w. ciii i'bein 'ri i' an diamagnetic g chane'i'n direct proporeiaihe P e i nxys n chan substantially myerseiy' w the absolute tern}pasture; and that of the diafn'agneticgass is substantiallydnvariablewith temperature, volunies maintained c assiest As the susceptibility ofmmes'g s substannauy additive "respastic; the part'i-iiolijihi'es'pisntg it is easy in ter'fio'calculate' thesusceptibility of a example flue gas'o'ntainin'g 10%" oxygen, atanyd'ir'ed prs'sure and temperature froniithe'fla tions ju'si'i'stated-f i sn Thus, according td'ith'ej invention, the suscep, tibility of the gassample-is determined, and the value obtainedis' suitably corrected forte'mpei'a= ture and pressure as indicated above, and the value soobtained is compared with the figures given in table above. Thecomparison is facilitated by plotting the values on a graph, as therelationship between oxygen content and susceptibility is linear for theordinary gases comprised in the fields of application of this invention.

Not only will we proceed to show how the process of the invention may becarried out, but also it will be shown how the operation described abovecan be done as completely mechanically as desired, so that correctionsfor temperature and also for pressure are automatically made and finalreadings obtained directly in terms of oxygen content, either as apartial pressure or a volume percentage. Also we will show how controlof oxygen concentration can be automatically achieved.

Reference is now made to the drawings accompanying this specification;therein:

Figure 1 shows a form of apparatus which is suitable;

Figure 2 shows a variation of detail in the apparatus of Figure l.

In Figure 1 an electromagnet i is excited by an alternating current coilH. The pole pieces in this instance are shaped to give maximum fieldstrength in a relatively small space between them; gradient of fieldstrength is of no particular importance. There are inserted into thefield between the pole pieces two rods, I2 and 13, which almost touch inthe strongest part of the field. These rods maintain a substantiallyconstant cross-sectional area until the limits of the strong portion ofthe magnetic field are reached, whereupon they taper out and terminateat the needles" of two ordinary pickups, I5 and 18, such as are used forphonograph record reproduction. The rods are positioned by supports I!and I8, which may be rubber collars or the like. The two pickups areconnected to an amplifier, at least the first stage of which is apush-pull stage, and the basic parts of which are schematicallyindicated in Figure 1. The pickups are connected with respect topolarity so that when both rods are mutually repelled or mutuallyattracted, the two grids of the first stage are given oppositepolarities so that an impulse results in the secondary of thetransformer [9.

Conversely, with such an arrangement, movement of the two rods in thesame direction, with unchanged mutual separation, will result in changesin primary currents in the transformer [9, which cancel each other andgive no impulse. Potentiometer 25 can be adjusted to balance outinequalities between the two outputs. An alternating current outputmeter is placed across the output of the amplifier, which may. ofcourse, contain more stages of amplification than shown if necessary.The output meter 29 is calibrated in units of oxygen partial pressure.An enclosure 2! is placed around the electromagnet and is fitted withtubulations 22 and 23 whereby the enclosure can readily be filled withthe gas to be tested.

The rods 12 and [3 are constructed of a hard, durable substance having asusceptibility which for best results is approximately within the rangeof that of the gases to be tested. A suitable material is analuminum-zinc alloy containing about 45% zinc, or a platinum tubecontaining a close fitting antimony rod, of suitable mutual proportions.Glass or plastic rod, containing a core of a sufficient proportion ofparamagnetic material such as platinum, aluminum, tourmaline, eboniteand the like may be used. of these, those which do not conductelectricity throughout the mass are preferable because damping by eddycurrents is thereby avoided. Here generally it is preferable to have thevolumar susceptibility of the rod or rods within the approximate limitsof l0 l0- to +l 10- volumar C. G. S. units.

The mode of operation of the apparatus of Figure 1 is as follows: When agas which is more paramagnetic than the rods 12 and i3, surrounds thelatter, the rods will tend to move out of the magnetic field, which ofcourse occurs when the magnet is excited by current during a portion ofthe alternating-current cycle. When the magnetic field is zero, asoccurs approximately at the time when the alternating current ischanging direction, the tendency to move out of the field will cease,and the rods will spring back into place. When the current is reversedduring the second half of the cycle, the magnetic field will again riseto a maximum and the rods will be repelled. Thus, if the currentenergizing the magnet has a frequency of cycles per second, the rodswill vibrate cycles per second. If the gas is less paramagnetic than therods, the latter will tend to move into the field during the period whenthe magnetic field is present.

Now the force attracting or repelling the rods is, other variables beingunchanged, directly proportional to the algebraic difference of thevolumar susceptibilities of the gas and the rod, and therefore a directfunction of the oxygen content of the gas. Since the E. M. F. developedby the pickups is a function of that force, and can be suitablyamplified and transformed into a meter reading, the ability of thisdevice to read oxygen directly is at once apparent. The meter may be ofthe indicating type, as shown in Figure 1 or it may be a recordingmeter. For the general case, an alternating current milliammeter isused, although a rectifying device such as a tube or copper oxidedisc-pile can be placed in the output circuit so that a direct currentmeter may be used. It is advantageous to have the meter scale calibrateddirectlyin units of oxygen concentration; also, the output of theamplifier can be connected to a control mechanism, as de-- scribed morefully hereinbelow.

A method of automatic temperature compensation incorporable into theapparatus of Figure 1 will now be described. Since the masssusceptibility of oxygen varies inversely as the first power of theabsolute temperature, and since the isobaric volume of oxygen alsovaries inversely with the first power of the absolute temperature, theisobaric volume susceptibility evidently varies inversely as the squareof the absolute temperature. Now for the region of ordinary roomtemperatures, this amounts to a change of approximately 0.67% per degreecentigrade. Accordingly, if a resistance 26 having a temperaturecoeificient of that amount is placed in the gas to be measured, and alsois simultaneously placed in the electrical circuit by means of leads 21and 28 so that it will change the output of the amplifier by thatamount,then the amplifier gain will be automatically compensated forchanges in temperature.

While nearly any frequency of alternating current may be used toenergize the magnet, ordinary 50 or 60 cycle current is particularlyconvenient in actual application. Whatever frequency is used, careshould be taken to adjust the resonant frequency of the mechanicalvibrating system to such a value as will assure smooth response to theenergizing force, in accordance with well-known laws of mechanicallyresonant systems.

It is desirable to make the system independent of externally imposedshocks, vibrations, accelerations and rotations so that installationswhere severe operating conditions prevail, such as in warships, arefeasible. This can be done in several ways, as now discussed in detail.First the arrangement of the armature rods I2 and I3, in Figure l, withthe pickup output connected in push-pull as described hereinabove,largely avoids such troubles. Moreover, both armature rods can be Lshaped and can be pivoted and so designed as to be in both dynamic andstatic balance; in fact such a design of the armature is particularlyadvantageous where only one armature rod is used. The general design ofsuch a pivoted armature is shown in Figure 2, where 30 and 3| are thepole pieces of the magnet, 32 is the pivoted armature with at least theportion 33 which projects into the strong part of the field being ofmaterial of suitable susceptibility, and 34 is the pivot, rotation aboutwhich point allows the end of the armature 33 to move in and out of themagnetic field. 35 is a single pickup, the leads of which, 36, areconnected to an amplifier, not shown.

Freedom of instrument reading from vibration can also be achieved forinstruments working on the general type of Figure 1 by causing theamplifier to be selective for the driving frequency of theelectromagnet. For example, a sharply peaked band pass filter may beincorporated into the amplifier circuit, which will pass only thefrequency generated by the magnetic field, and will not pass thefrequency vibrating armature which as explained hereinabove will ingeneral be different from the former.

Again, some of the alternating current from the source which energizesthe electromagnet can be passed through a phase shifting circuit, thenrectified, and, without filtering, used to supply grid or plate voltagefor some convenient tube in the amplifying circuit, so that that tubeamplifies only those impulses which are of a frequency and phasederivable from the action of the pulsating magnetic field on thearmature assembly. Of course, the exact manner of application of thesevarious amplifying current refinements will be evident to an electronicengineer, and need not be detailed herein.

In most cases where oxygen concentrations are of interest it isdesirable to control the processes or conditions giving rise to theparticular concentrations encountered. Usually an oxygen concentrationwithin certain fixed limits indicates optimum operation; when thoselimits are exceeded, it is desirable to change operating conditions tobring the concentration back to normal. Thus, in a gas-fired boilerflue, less than about 1% oxygen indicates the necessity of increasingthe air-gas input ratio if efiicient combustion is to be maintained. Ifthe flue gas rises above about 3 oxygen, then the air-gas ratio shouldbe reduced. Again, in supercharged airplane cabins. submarine interiors,or the like, the oxygen concentration must be controlled within certainlimits.

The devices embodying the present invention can be readily adapted tosuch an automatic control, by causing the oxygen content indicator tooperate relays or the like which are in turn connected to the primaryvariable mechanisms, such as oil, gas, air and oxygen inlet valves,dampers, coal stokers, and the like.

It will be understood that while several devices have been described indetail hereinabove, multitudinous modifications can be made thereinwithin the broad scope of the invention. Also, while as many separateembodiments as conveniently desirable within the proper limits ofconciseness have been disclosed, it will be understood that theinvention broadly embraces many other modifications, and is notnecessarily limited to the particular devices shown herein.

We claim:

1. An apparatus for the determination of the oxygen content of a mixedgas containing oxygen, comprising, an alternating current magnet,providing an alternating magnetic field, an object capable of beingsurrounded by said gas, and positioned in said alternating magneticfield, so that one portion is in a relatively strong part of the fieldand another portion is in a relatively weak part, restraining means tosubstantially inhibit translational motion of the object whilepermitting it to vibrate, and a vibration receptor operatively connectedwith said object, and oxygen indicating means operatively connected tosaid vibration receptor.

2. An apparatus of the type of claim 1, in which the object has a volumemagnetic susceptibility approximately within the range of 10 10- to 10-C. G. S. units.

3. An apparatus of the type of claim 1, in which the object isstatically and dynamically balanced.

4. Apparatus for measuring the oxygen content of a gas, comprising meansforming a chamber for holding the gas, a magnet having a gap disposedwithin said chamber, means for energizing said magnet with alternatingcurrent, armatures movably mounted within said gap, a pickup connectedwith said armature, a voltage amplifier connected to said pickup, and anindicating member connected with said voltage amplifier.

5. Apparatus of the type of claim 4, in which the armature material hasvolume magnetic susceptibility approximately within the range of 10 10-to 150 10* C. G. S. units.

EDWARD L. KELLS. DELMAR H. LARSEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,416,344 Pauling Feb. 25, 19472,467,211 Hornfeck Apr. 12, 1949

